Welcome to

It is the members who make this best place for FJ related content on the internet.

Main Menu

New petcock and intermittent starting issues...

Started by CatTomb, May 21, 2013, 11:29:28 PM

Previous topic - Next topic

big r

You need to do a flapectomy on the gas cap. It's in the files section not to sure where. Big R.


Quote from: big r on May 24, 2013, 09:30:58 PM
You need to do a flapectomy on the gas cap. It's in the files section not to sure where. Big R.

Here's the link...
"Never forget that only dead fish swim with the stream." Malcolm Muggeridge, Chronicles of Wasted Time (1972)


Quote from: Brian Penney on May 24, 2013, 08:48:53 PM
I'm having the same sort of "lack of fuel" issues, my lines are not pinched but I will try the new vacuum hose. When my tank is low on fuel "Still lots of fuel in the tank" it starts to stumble, I flip the reserve switch and it doesn't make any difference, starves for fuel then I push it to the gas station, fill-er up and away I go. BUT when I open my tank to add fuel it sucks air, bigtime! Where am I getting this negative pressure from? Why does it starve for fuel with a 1/4  tank?

"Flapectomy" or repair it....  Common problem. Easy to fix.
Life isn't about having the best, but about making the best of what you have...

1990 FJ 1200

Pat Conlon

Yea, you have a tank venting issue. You need to do some surgery on your cap.
As you fill your tank with gas and the cap is open, air escapes out of the tank as the tank fills. Then you close your cap and away you you ride the level of gas drops in the tank but air can't get in so it creates a negative pressure.
The negative pressure builds up as the gas level gets to the bottom causing the flow of gas to diminish. It's actually holding the gas in the tank.
Gravity fed FJ's are fussy...very fussy...about gas flow. The fuel lines *have to* be routed correctly.
The tank has to be vented to atmospheric pressure allowing gravity to do its job.....and no filter or obstruction in the fuel line to impede the flow.

Just a couple of reasons Yamaha converted over to fuel pumps in the later FJ's
No more vacuum petcock shenanigans and now you can install a real fuel filter keeping shit out of your carbs.

Hope this explanation helps.  Cheers.
1) Free Owners Manual download:
2) Don't store your FJ with E10 fuel
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire:
Fuel line:


Has anyone had any luck with an in-line fuel filter for the 84-85 FJ setup?

Mark Olson

no luck with in line filters... there is one on the petcock.

gravity fed fuel fj's get real touchy at 1/4 tank if you are at freeway speeds or high rpm.

easily fixed with a flapperectomy on the gas cap.

an extra tip: Magnetic tank bags cover the vent for gas cap and will also cause fuel starvation.

all this is solved with a gas cap flapperectomy.

or stick a slurpee straw between the bag and tank for a vent. :wacko3:
Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"